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Anaesthesia and Pain Management > Maintenance Agents > Flashcards

Maintenance Agents Flashcards

1
Q

What is inhalation anaesthesia?

A
  • Induction: Usually with an injectable and can be with a gas
  • Maintenance: Usually with an inhalational agent and can with injectable
  • For both: Part of the gas provided in nitrous oxide or a liquid vaporised into the mixed gas
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2
Q

What are volatile agents?

A
  • Liquid anaesthetic agents that are vaporised into gases, which are then inhaled by the patient
  • A vaporiser is a device that adds volatile agent to a carrier gas
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3
Q

What are the ideal properties of volatile agents?

A
  • Chemically stable
  • Non-flammable
  • No environmental hazard
  • Inexpensive
  • High potency
  • Low blood solubility
  • Minimal metabolism
  • Minimal toxicity
  • No cardiorespiratory side effects
  • Analgesia
  • Easily administered
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4
Q

What are the advantages of inhalation agents?

A
  • Administered in oxygen through ET tube
  • Rapid action
  • Change in depth of anaesthetic rapid
  • Rapid recovery
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5
Q

What are the disadvantages of inhalation agents?

A
  • Anaesthetic machine costly and requires full understanding by user
  • Workplace pollution
  • Dose dependent cardiopulmonary depression
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6
Q

What are the pharmocokinetics of inhalation agents?

A
  • Agent is inhaled and passed into lungs
  • Diffuses into the pulmonary circulation
  • Travels around the body via the circulatory system and is distributed to the tissues
  • Depending on agent solubility, it will diffuse back into the blood and be eliminated by the lungs
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7
Q

What are the factors that affect gaseous uptake?

A
  • Inspired concentrations of the agent
  • Alveolar concentration
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8
Q

How do inspired concentrations affect gaseous uptake?

A
  • Vaporiser setting: the higher the % on the dial, the more concentrated the volatile agents
  • FGF: a high FGF will affect the volume of volatile agents in a rebreathing system
  • Function of the breathing system: rebreathing systems are bulky and have lots of components meaning that it takes longer for higher concentrations to be reached
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9
Q

What is alveolar concentration?

A
  • This is the partial pressure
  • Used as a blood: gas partition coefficient
  • Reliant on good alevolar ventilation and pulmonary circulation
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10
Q

What is the blood : gas partition coefficient?

A
  • The measure of the distribution of the inhalation agent between the blood and gas phases within the body
  • Low solubility: does not dissolve in the blood so rapid induction and recovery
  • High solubility: dissolves more readily in the blood, so slow induction and recovery
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11
Q

What is potency?

A
  • Is expressed as the minimum alveolar concentration (MAC value)
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12
Q

What is a MAC value?

A
  • The amount of volatile gas that is needed to keep 50% of patients asleep when exposed to a standard noxious stimuli
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13
Q

What increases the MAC value?

A
  • Hyperthermia
  • Catecholamines
  • Hyperthyroidism
  • Hypernatremia
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14
Q

What decreases the MAC value?

A
  • Hypothermia
  • Hypoxaemia
  • Hypercapnia
  • Drugs that affect CNS
  • Analgesia agents
  • Pregnancy
  • Old age
  • Hypotension
  • Hypothyroidism
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15
Q

What factors affect the elimination of inhalants?

A
  • CNS concentrations low enough, the patient will start to regain consciousness
  • Newer gases almost 100% eliminated through exhalation
  • Older gases 25% is metabolised
  • Removal of agent is determined by B : G pCE
  • Can speed up elimination in rebreathing system by turning off the gas and increasing the oxygen flow
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16
Q

What is the inhalant effect on the cerebrum?

A
  • Decrease metabolic rate
  • Decrease in cerebral oxygen concentration
  • Decrease in cerebral blood flow
    -Cerebral vasodilation
  • Increase in blood volume
17
Q

What is the inhalant effect on the cardiovascular system?

A
  • CV depression is a major side
  • This is dose dependent
    -Cardiac output, systemic vascular resistance and arterial BP, due to decreased myocardial contractility and vasodilation
18
Q

What is the inhalant effect on the respiratory system?

A
  • Dose dependent respiratory depression
  • Could lead to hypercapnia
  • Decrease in minute volume
  • Decrease in respiratory rate
  • Decrease in tidal volume
19
Q

What is the inhalant effect on the renal and hepatic system?

A
  • Perfusion is decreased due to hypotension
  • Renal perfusion issues may lead to decreased urine output
  • Sevoflurane with rebreathing systems can react with soda-line, which makes compound A (is nephrotoxic in rats)
  • Decreased perfusion to the liver may lead to decreased drug metabolism
20
Q

What is halothane?

A
  • Very potent halogenated hydrocarbon
  • Requires preservative
  • Does not decompose in presence of warm soda lime
  • Respiratory and cardiovascular depressant
  • Metabolised by liver (20-25%)
21
Q

What is isoflurane?

A
  • Fluorinated ether
  • Very potent
  • Delivered using a precision out of circuit vaporiser
  • Strong pungent colour
  • Respiratory and cardiovascular depressant
  • Low solubility
  • Under 1% metabolised by patient
22
Q

What is sevoflurane?

A
  • Fluorinated ether
  • Slightly less potent than isoflurane
  • Requires different vaporiser to isolflurane
  • Metabolised to produce fluoride ions
  • Less soluble than isoflurane
  • Cardiovascular and respiratory depressant
  • 3% metabolised
23
Q

What is desflurane?

A
  • Fluorinated ether
  • Needs specialised vaporiser
  • Expensive
24
Q

What is nitrous oxide?

A
  • Gaseous inhalant
  • Used in combo with more potent inhalant such as halothane
  • Low solubility so rapid transfer
  • Cannot achieve true anaesthesia alone as MAC values are high
25
Q

What are the side effects of using nitrous oxide?

A
  • Mild sympathetic stimulation
  • Diffuses into gas filled spaces
  • Diffusion hypoxia, so adequate oxygen required during recovery
26
Q

What is the nitrous oxide second gas effect?

A
  • Nitrous oxide will increase the rate of uptake of other inhalational agents into the blood stream and therefore an appropriate level of anaesthesia will be reached more quickly
27
Q

What is nitrous oxide diffusion hypoxia?

A
  • Caused by rapid movement of gas
  • When recovering, nitrous oxide should be switched off and and oxygen should be maintained
  • if not, oxygen can reach dangerously low levels in alveoli as nitrous diffuses out of blood stream
28
Q

What is occupational exposure?

A
  • Gas leaking into the room, due to disconnection of the patient and not flushing out the anaesthetic circuit, poorly fitted mask, underinflated ETT cuff and during recovery from GA
  • Can causes mutagenic, carcinogenic and teratogenic effects
29
Q

What are the inhalational exposure issues?

A
  • Spontaneous abortion
  • Fertility issues
  • Minor congenital abnormalities
  • Leukaemia and lymphoma
  • Liver/renal disease
  • Effects on the immune system

Anaesthesia and Pain Management (7 decks)

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